Question
In execution compression test for concrete, have to test cubes .Test cylinders be approved?

Answer
Essentially, results of compression test carried out by using cubes are advanced than that by cylinders. In compression test, failure mode is in form of tensile splitting induced by uniaxial compression. Though, as concrete samples tend to enlarge laterally under compression, friction developed at concrete-machine interface generates forces which apparently increase compressive strength of concrete. Though, when ratio of height to width of sample increases, effect of shear on compressive strength becomes smaller. These explain why results of compression test by cylinders are lower than that of cubes.